Shock absorber

ABSTRACT

A shock absorber includes a damping force adjustment mechanism having a flow passage that allows the fluid from a cylinder, a valve seat, a valve body, and a stepper motor that adjusts a flow passage area by driving the valve body. A valve body position in which step-out may occur in the stepper motor if the valve body is moved further toward the valve seat therefrom is set as a step-out boundary position, a zone between a seated position in which the valve body is seated on the valve seat and the step-out boundary position is set as a step-out zone, and when the valve body is to be moved to the seated position through the step-out zone, the stepper motor is energized to move the valve body by a distance that is at least twice a distance to the seated position.

TECHNICAL FIELD

This invention relates to an improvement in a shock absorber.

BACKGROUND ART

JP2008-14431A discloses a shock absorber that is installed in a frontfork of a motorcycle to perform damping force adjustment using a motor.The shock absorber includes a shock absorber main body having a cylindercoupled to an outer tube, a piston that is inserted in the cylinder tobe free to slide and divides an interior of the cylinder into acontraction side chamber and an expansion side chamber, and a piston rodthat is inserted into the cylinder such that one end thereof is coupledto an inner tube, which is inserted into the outer tube to be free toslide, and another end is coupled to the piston. The shock absorberfurther includes a passage connecting the contraction side chamber andthe expansion side chamber of the shock absorber main body, a checkvalve provided midway in the passage to allow only a flow traveling fromthe contraction side chamber toward the expansion side chamber orconversely to allow only a flow traveling from the expansion sidechamber toward the contraction side chamber, a needle valve providedmidway in the passage, and a stepper motor that is fixed to the otherend side of the piston rod in order to drive the needle valve.

During expansion, the shock absorber generates damping force by applyingresistance to a flow of working oil using a piston valve provided in thepiston, and during contraction, the shock absorber generates dampingforce by applying resistance to a flow of working oil flowing out of thecylinder into a reservoir using a base valve provided in an end portionof the cylinder.

Further, in this shock absorber, the working oil is caused to flowthrough the passage either only during expansion or only duringcontraction by an action of the check valve. By having the needle valveapply resistance to this flow of working oil, the needle valve generatesdamping force cooperatively during either expansion or contraction ofthe shock absorber. Furthermore, by driving the needle valve using themotor, the damping force generated by the needle valve can be varied.

Hence, the needle valve performs a damping function only duringexpansion or contraction of the shock absorber. A front fork thatstraddles a vehicle wheel of a motorcycle typically straddles thevehicle wheel in a left-right pair. Therefore, the needle valve of theshock absorber built into one front fork performs the damping functionduring expansion, and the needle valve of the shock absorber built intothe other front fork performs the damping function during contraction.As a result, the expansion side damping force and the contraction sidedamping force can be adjusted by the front fork as a whole.

According to this shock absorber, the flow of working oil passingthrough the needle valve always travels in one direction and istherefore a stable flow. As a result, the damping force generated by theshock absorber can be adjusted accurately.

SUMMARY OF INVENTION

Incidentally, in a case where the passage is blocked by the needlevalve, the needle valve must be driven so as to overcome a fluid forceand a pressure generated by the working oil flow in order to block thepassage. To block the passage while the shock absorber is operative andthe working oil is flowing through the passage, therefore, a steppermotor capable of outputting a large torque must be used. To cause thestepper motor to output a large torque, a size and a cost of the steppermotor must be increased, and it may therefore be necessary to sacrificeeconomic efficiency and ease of installation in a vehicle.

When the passage is blocked while the working oil flows through thepassage, the needle valve can be driven by a comparatively small torqueup to a point immediately before the passage is blocked, and in thiscondition, step-out is unlikely to occur. In a conventional shockabsorber, therefore, the passage is not blocked completely so that astepper motor having a comparatively small maximum torque can be used,and in so doing, the problem described above can be solved.

With this configuration, however, the passage cannot be blocked, andtherefore a flow passage variation width of the needle valve inevitablydecreases. Accordingly, a damping force adjustment width of the shockabsorber decreases, and when step-out occurs in the stepper motor duringtravel, the step-out cannot be corrected during travel. As a result, thedamping force cannot be adjusted correctly.

This invention has been designed in consideration of the problemsdescribed above, and an object thereof is to enable the use of a small,inexpensive motor, and to increase a damping force adjustment width bymaking step-out correction possible.

According to one aspect of this invention, a shock absorber includes: ashock absorber main body having a cylinder housing a fluid, a pistonthat is inserted into the cylinder to be free to slide and divides aninterior of the cylinder into a contraction side chamber and anexpansion side chamber, and a piston rod inserted into the cylinder andcoupled to the piston; and a damping force adjustment mechanism having aflow passage that allows the fluid from the cylinder to pass during onlyone of an expansion operation and a contraction operation of the shockabsorber main body, a valve seat provided midway in the flow passage, avalve body capable of advancing and retreating relative to the valveseat, and a stepper motor that is configured to adjust a flow passagearea by driving the valve body to advance and retreat relative to thevalve seat. A valve body position in which step-out may occur in thestepper motor if the valve body is moved further toward the valve seattherefrom is set as a step-out boundary position, and a zone between aseated position in which the valve body is seated on the valve seat andthe step-out boundary position is set as a step-out zone. When the valvebody is to be moved to the seated position through the step-out zone,the stepper motor is energized to move the valve body by a distance thatis at least twice a distance to the seated position.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a shock absorber according to anembodiment of this invention.

FIG. 2 is an enlarged sectional view of a damping force adjustmentmechanism provided in the shock absorber according to this embodiment ofthis invention.

FIG. 3 is a view illustrating a step-out zone and a non-step-out zone ofthe shock absorber according to this embodiment of this invention.

FIG. 4 is a view illustrating expansion and contraction generated byvibration of the shock absorber according to this embodiment of thisinvention.

FIG. 5 is a view illustrating a plurality of valve body stop positionsin the shock absorber according to this embodiment of this invention.

DESCRIPTION OF EMBODIMENTS

Referring to the figures, a shock absorber 1 according to an embodimentof this invention will now be described.

As shown in FIG. 1, the shock absorber 1 includes a shock absorber mainbody D having a cylinder 2 housing a fluid, a piston 3 that is insertedinto the cylinder 2 to be free to slide and divides an interior of thecylinder 2 into a contraction side chamber R1 and an expansion sidechamber R2, and a piston rod 4 that is inserted into the cylinder 2 andcoupled to the piston 3. The shock absorber 1 also includes a dampingforce adjustment mechanism V having a flow passage 5 that allows thefluid to pass only when the shock absorber main body D expands, a valveseat 6 provided midway in the flow passage 5, a valve body 7 capable ofadvancing and retreating relative to the valve seat 6, and a steppermotor 8 that adjusts a flow passage area by driving the valve body 7 toadvance and retreat relative to the valve seat 6.

Referring to FIGS. 1 and 2, each part will now be described in detail.

The shock absorber main body D is housed in a front fork F constitutedby a vehicle body side tube 10 coupled to a vehicle body, not shown inthe figures, of a saddle-ridden vehicle such as a motorcycle, and anaxle side tube 11 that is coupled to an axle, not shown in the figures,of the saddle-ridden vehicle and inserted into the vehicle body sidetube 10 to be free to slide. More specifically, the shock absorber mainbody D is interposed between the vehicle body side tube 10 and the axleside tube 11 by coupling the piston rod 4 to the vehicle body side tube10 and coupling the cylinder 2 to the axle side tube 11. The shockabsorber main body D is housed in the front fork F, which is enclosed bythe vehicle body side tube 10 and the axle side tube 11. It should benoted that in the shock absorber main body D, the front fork F is aninverted front fork in which the axle side tube 11 is inserted into thevehicle body side tube 10, but a normal front fork in which the vehiclebody side tube 10 is inserted into the axle side tube 11 may be usedinstead.

A suspension spring 12 is interposed between the piston rod 4 and thecylinder 2 of the shock absorber main body D. The suspension spring 12generates elastic force in a direction for separating the vehicle bodyside tube 10 and the axle side tube 11 via the shock absorber main bodyD, or in other words a direction for expanding the front fork F. Thevehicle body of the saddle-ridden vehicle is elastically supported bythe suspension spring 12.

Next, the shock absorber main body D installed in the front fork F willbe described.

As shown in FIG. 1, the shock absorber main body D includes the cylinder2, which is coupled to the axle side tube 11, the piston 3 that isinserted into the cylinder 2 to be free to slide and divides theinterior of the cylinder 2 into two working chambers, namely thecontraction side chamber R1 and the expansion side chamber R2, and thepiston rod 4 that is coupled to the piston 3 at one end and coupled tothe vehicle body side tube 10 at another end. The shock absorber mainbody D also includes a damping passage 13 that is provided in the piston3 to connect the contraction side chamber R1 to the expansion sidechamber R2 and apply resistance to a flow of fluid passing through, anda bottom member 14 provided on a lower end of the cylinder 2. The bottommember 14 includes a contraction side damping passage 15 that appliesresistance to a flow of fluid traveling from the expansion side chamberR2 toward a reservoir R, and a suction passage 16 that allows the fluidto flow only from the reservoir R toward the contraction side chamber. Afluid such as working oil is charged into the contraction side chamberR1 and the expansion side chamber R2 as the fluid, while the fluid and agas are charged into the reservoir R.

More specifically, the cylinder 2 is fixed to a bottom portion of theaxle side tube 11, which is formed in the shape of a closed-endcylinder, via the bottom member 14, which is fitted to the lower endthereof. Further, a rod guide 17 that supports the piston rod 4 axiallyto be free to slide is provided on an upper end of the cylinder 2. Thepiston rod 4 includes a piston rod main body 4 a that is formed in atubular shape and has a hollow portion 4 b, and a piston couplingportion 4 c that is fixed to one end portion (a lower end in FIG. 1) ofthe piston rod main body 4 a in order to hold the piston 3. Another endportion (an upper end in FIG. 1) of the piston rod 4 is fixed to anupper end of the vehicle body side tube 10 via a valve housing 9 housingthe valve body 7 of the damping force adjustment mechanism V. The pistoncoupling portion 4 c includes a connecting passage 4 d connecting thehollow portion 4 b to the contraction side chamber R1, and a check valve4 e provided midway in the connecting passage 4 d to allow the fluid toflow only from the contraction side chamber R1 toward the hollow portion4 b. The annular piston 3 positioned on the lower end of the pistoncoupling portion 4 c in FIG. 1 is fixed to the piston coupling portion 4c using a piston nut 24.

The aforesaid suspension spring 12 is interposed between a tubularspring bearing 18 provided on an outer periphery of the valve housing 9,and the rod guide 17. The shock absorber main body D is biased in anexpansion direction by the suspension spring 12, whereby the front forkF is also biased in the expansion direction.

The piston 3 is fixed to a lower end portion of the piston rod 4positioned at the lower end in FIG. 1. The damping passage 13 providedin the piston 3 includes a passage 13 a connecting the contraction sidechamber R1 to the expansion side chamber R2, and a damping valve 13 bprovided midway in the passage 13 a. The damping passage 13 appliesresistance to a flow of fluid passing through. Here, the damping valve13 b is a throttle valve. Accordingly, the damping passage 13 allows thefluid to flow both from the contraction side chamber R1 toward theexpansion side chamber R2 and from the expansion side chamber R2 towardthe contraction side chamber R1. This invention is not limited to thisconfiguration, however, and instead, two or more passages may beprovided such that a damping valve that allows the fluid to flow onlyfrom the contraction side chamber R1 toward the expansion side chamberR2 is provided in one passage and a damping valve that allows the fluidto flow only from the expansion side chamber R2 toward the contractionside chamber R1 is provided in another passage.

The reservoir R is formed in a space between the shock absorber mainbody D and the front fork F. The fluid and a gas are charged into thereservoir R. The contraction side damping passage 15 formed in thebottom member 14 includes a passage 15 a connecting the expansion sidechamber R2 to the reservoir R, and a damping valve 15 b that allows thefluid to flow only from the expansion side chamber R2 toward thereservoir R and applies resistance to the flow of fluid passing through.The contraction side damping passage 15 is a one-way passage that allowsthe fluid to flow only from the expansion side chamber R2 toward thereservoir R. Meanwhile, the suction passage 16 formed in the bottommember 14 includes a passage 16 a connecting the expansion side chamberR2 to the reservoir R, and a check valve 16 b that allows the fluid toflow only from the reservoir R toward the expansion side chamber R2. Thesuction passage 16 is a one-way passage that allows the fluid to flowonly from the reservoir R toward the expansion side chamber R2, i.e. inan opposite direction to the contraction side damping passage 15.

Next, the damping force adjustment mechanism V will be described.

As described above, the damping force adjustment mechanism V includesthe flow passage 5 that connects the contraction side chamber R1 to thereservoir R and allows the fluid to pass only from the contraction sidechamber R1 toward the reservoir R, the valve seat 6 provided midway inthe flow passage 5, the valve body 7 that is capable of advancing andretreating relative to the valve seat 6, and the stepper motor 8 thatadjusts the flow passage area by driving the valve body 7 to advance andretreat relative to the valve seat 6.

More specifically, the flow passage 5 includes the hollow portion 4 band the connecting passage 4 d provided in the piston rod 4, a hollowportion 9 a that is provided in the valve housing 9 coupled to an endportion (the upper end portion in FIG. 1) of the piston rod 4 so as tocommunicate with the hollow portion 4 b, and a lateral hole 9 b thatconnects the hollow portion 9 a to the reservoir R. The flow passage 5connects the contraction side chamber R1 to the reservoir R, and allowsthe fluid to pass only from the contraction side chamber R1 into thereservoir R using the check valve 4 e provided midway in the connectingpassage 4 d. The check valve that sets the flow passage 5 as a one-waypassage may be provided in a location other than the piston couplingportion 4 c. More specifically, the check valve may be provided in thehollow portion 4 b of the piston rod main body 4 a, for example. Thecheck valve may also be provided at an open end of the hollow portion 4b in an end portion (the upper end portion in FIG. 1) of the piston rodmain body 4 a.

As shown in FIG. 2, the valve housing 9 is formed in a tubular shape.The valve housing 9 includes the hollow portion 9 a formed in aninterior thereof, the lateral hole 9 b that opens sideward so as tocommunicate with the hollow portion 9 a, and a flange 9 g provided on anouter periphery. Further, the hollow portion 9 a includes a smalldiameter portion 9 c formed with a small inner diameter further toward apiston rod side (a lower side in FIG. 1) than an intersection portionwith the lateral hole 9 b, a lateral hole intersection portion 9 d whichis connected to the small diameter portion 9 c, has a larger innerdiameter than the small diameter portion 9 c, and intersects the lateralhole 9 b, a valve housing portion 9 e which is formed with a largerinner diameter than the lateral hole intersection portion 9 d and intowhich the valve body 7 is inserted to be free to slide, and an enlargeddiameter portion 9 f formed with a larger inner diameter than the valvehousing portion 9 e. The valve seat 6 is formed in the hollow portion 9a by a step serving as a boundary between the small diameter portion 9 cand the lateral hole intersection portion 9 d. In other words, the valveseat 6 is formed in the valve housing 9 and provided on a tip end of thepiston rod 4.

The valve body 7 includes a trunk portion 7 a that slides against thevalve housing portion 9 e, a valve portion 7 b that extends from thetrunk portion 7 a toward the valve seat 6 side and has an outer diameterwhich is smaller than the trunk portion 7 a and larger than the innerdiameter of the small diameter portion 9 c, a needle-shaped valve head 7c that extends from a tip end (a lower end in FIG. 1) of the valveportion 7 b and can be inserted into the small diameter portion 9 c, andan annular seal ring 7d that is attached to an outer periphery of thetrunk portion 7 a so as to slide against an inner periphery of the valvehousing portion 9 e. The valve body 7 is biased in a separationdirection from the valve seat 6 by a coil spring 19 interposed betweenan end portion (a lower end in FIG. 1) of the trunk portion 7 a and astep formed in the hollow portion 9 a as a boundary between the lateralhole intersection portion 9 d and the valve housing portion 9 e.

The valve body 7 is housed in the hollow portion 9 a to be capable ofadvancing and retreating relative to the valve seat 6, or in other wordscapable of moving in an axial direction. The valve body 7 is provided tobe capable of advancing and retreating relative to the valve seat 6 whendriven by the stepper motor 8. As shown in FIG. 2, when the valve body 7is driven such that an outer periphery of an end portion (a lower end inFIG. 1) of the valve portion 7 b of the valve body 7 opposing the valveseat 6 moves to a seated position contacting the valve seat 6, the flowpassage 5 is blocked. When the valve body 7 moves away from the valveseat 6 from a condition in which the flow passage 5 is blocked in thismanner, the valve portion 7 b separates from the valve seat 6, causing agap to form, and as a result, the flow passage 5 is opened.

Further, in a condition where the valve portion 7 b is separated fromthe valve seat 6 such that the flow passage 5 is open, a gap between thevalve head 7 c and an inner edge of the valve seat 6 increases as thevalve portion 7 b separates from the valve seat 6. As a result, the flowpassage area of the damping force adjustment mechanism V can be varied.In other words, the flow passage area of the damping force adjustmentmechanism V can be modified in accordance with a positional relationshipbetween the valve body 7 and the valve seat 6.

When the valve body 7 moves to a maximum separation position in whichthe valve body 7 is furthest separated from the valve seat 6, the flowpassage area of the damping force adjustment mechanism V reaches amaximum. When the valve body 7 moves to the seated position so as to beseated on the valve seat 6, the flow passage 5 is completely blocked,and therefore the flow passage area is zero. When the flow passage 5 isopen, the contraction side chamber R1 and the expansion side chamber R2communicate, and therefore, when the shock absorber 1 performs anexpansion operation in this condition, the fluid passes through the flowpassage 5 so as to be discharged into the reservoir R. Hence, resistanceis applied to the flow of fluid in accordance with the flow passage areaof the damping force adjustment mechanism V.

Next, a driving part that causes the valve body 7 to advance and retreatrelative to the valve seat 6 will be described.

As noted above, the valve body 7 is driven by the stepper motor 8. Afeed screw mechanism S is interposed between the stepper motor 8 and thevalve body 7. The feed screw mechanism S drives the valve body 7 byconverting a rotary motion of the stepper motor 8 into anadvancing/retreating direction motion of the valve body 7. The feedscrew mechanism S includes a screw member 20 coupled to be incapable ofrotating but capable of moving in the axial direction to a shaft 8 a ofthe stepper motor 8, which is fitted to the enlarged diameter portion 9f of the hollow portion 9 a of the valve housing 9, and a nut member 21which is formed in a tubular shape and fixed to the enlarged diameterportion 9 f of the hollow portion 9 a, and to which the screw member 20is screwed.

More specifically, the screw member 20 is formed in a shaft shape, andincludes a shaft insertion hole 20 a that is open from a stepper motor 8side end portion serving as a base end side and a screw portion 20 bprovided on an outer periphery of an anti-motor side end portion servingas a tip end side. The screw member 20 is formed such that across-section of the shaft insertion hole 20 a does not take the shapeof a perfect circle. A cross-section of the shaft 8 a of the steppermotor 8 is shaped to fit the cross-section of the shaft insertion hole20 a.

The nut member 21 is formed in a tubular shape and fixed to the enlargeddiameter portion 9 f of the hollow portion 9 a. A screw portion 21 athat is screwed to the screw portion 20 b of the screw member 20 isprovided in an inner periphery of the nut member 21. The screw member 20is screwed to the nut member 21 such that a tip end thereof projectsfrom a lower end of the nut member 21 and contacts the valve body 7.

Hence, when the stepper motor 8 is driven, the shaft 8 a rotates,causing the screw member 20 to rotate relative to the nut member 21. Asa result, the shaft 8 a moves in the axial direction (a verticaldirection in FIG. 1) relative to the nut member 21. Meanwhile, the valvebody 7 is biased in the separation direction from the valve seat 6 bythe coil spring 19, as described above. Therefore, when the steppermotor 8 is driven to move the screw member 20 to the valve seat 6 side,the valve body 7 is pushed by the screw member 20 so as to advance tothe valve seat 6 side. Conversely, when the stepper motor 8 is driven tomove the screw member 20 in the separation direction from the valve seat6, the valve body 7 is pushed by the coil spring 19 so as to retreatfrom the valve seat 6.

The stepper motor 8 is attached to the outer periphery of the valvehousing 9 by a screw portion provided on an outer peripheral sidethereof. The stepper motor 8 is disposed to project from an upper endopening portion of the vehicle body side tube 10. The stepper motor 8 issandwiched between an annular outer peripheral nut member 22 that isengaged to the flange 9 g and a closed-top tube-shaped cap 23 that isscrewed to the outer peripheral nut member 22 so as to cover an open endof the valve housing 9, and thus fixed to the valve housing 9. The cap23 includes an opening portion 23 a that opens sideward. A connector 8 bof the stepper motor 8 faces the outside through the opening portion 23a in the cap 23. Hence, the connector 8 b of the stepper motor 8 and anexternal power supply, not shown in the figures, can be connected to apower line, not shown in the figures, via the opening portion 23 a, andas a result, power can be fed to the stepper motor 8 from the exteriorof the vehicle body side tube 10.

During expansion of the shock absorber 1, in which the piston 3 moves inone direction (upward in FIG. 1) relative to the cylinder 2, resistanceis applied to the flow of fluid moving from the contraction side chamberR1, which is caused to contract by the piston 3, into the expansion sidechamber R2 by the damping passage 13, and resistance is applied to theflow of fluid traveling from the contraction side chamber R1 toward thereservoir R by the damping force adjustment mechanism V. Duringexpansion, therefore, the shock absorber 1 generates expansion sidedamping force using the damping passage 13 and the damping forceadjustment mechanism V. Fluid is supplied to the expansion side chamberR2, which is enlarged during expansion, from the reservoir R via thesuction passage 16 provided in the bottom member 14. As a result, volumevariation in the cylinder 2 occurring when the piston rod 4 retreatsfrom the cylinder 2 during expansion of the shock absorber 1 iscompensated for.

During contraction of the shock absorber 1, on the other hand, in whichthe piston 3 moves in another direction (downward in FIG. 1) relative tothe cylinder 2, resistance is applied to the flow of fluid moving fromthe contraction side chamber R1, which is caused to contract by thepiston 3, into the expansion side chamber R2 by the damping passage 13.Further, an amount of fluid corresponding to a volume reduction in thecylinder 2 caused by infiltration of the cylinder 2 by the piston rod 4is discharged from the contraction side chamber R1 into the reservoir Rvia the contraction side damping passage 15 of the bottom member 14.Accordingly, volume variation in the cylinder 2 occurring when thepiston rod 4 infiltrates the cylinder 2 during contraction of the shockabsorber 1 is compensated for, and resistance is also applied to theflow of fluid by the contraction side damping passage 15. Hence, duringcontraction, the shock absorber 1 generates contraction side dampingforce using the damping passage 13 and the contraction side dampingpassage 15. At this time, the fluid is prevented from flowing throughthe flow passage 5, and therefore the damping force adjustment mechanismV does not contribute to generation of the contraction side dampingforce.

Furthermore, the flow passage area of the damping force adjustmentmechanism V can be varied by driving the valve body 7. With the shockabsorber 1, therefore, the expansion side damping force generated duringexpansion can be adjusted.

Here, a case of damping force adjustment in which the flow passage 5 iscompletely blocked by energizing the stepper motor 8 to drive the valvebody 7 from a condition in which the valve body 7 is separated from thevalve seat 6 such that the flow passage 5 is open will be investigated.

When the shock absorber 1 performs an expansion operation such that thefluid passes through the flow passage 5, the valve body 7 is caused toapproach the valve seat 6, leading to a gradual reduction in the flowpassage area of the damping force adjustment mechanism V. Accordingly, aresultant force of a thrust generated by a pressure (to be referred tohereafter as an “upstream pressure”) in the flow passage 5 on anupstream side of the damping force adjustment mechanism V and a fluidforce generated by a flow of fluid passing between the valve body 7 andthe valve seat 6 acts in a direction for separating the valve body 7from the valve seat 6. The upstream pressure increases as the flowpassage area of the damping force adjustment mechanism V decreases.Further, as the flow passage area of the damping force adjustmentmechanism V decreases, a flow speed of the passing fluid increases,leading to an increase in the fluid force. Hence, the resultant force ofthe upstream pressure and the fluid force increases as the flow passagearea of the damping force adjustment mechanism V decreases.

A maximum flow rate of the fluid passing through the flow passage 5 anda maximum value of the upstream pressure are assumed in advance fromspecifications of the vehicle to which the shock absorber 1 is appliedand a damping characteristic required of the shock absorber 1. Astep-out boundary position, which is a valve body position at whichstep-out may occur in the stepper motor 8 in a situation where the flowpassage area is reduced as the valve body 7 approaches the valve seat 6and the valve body 7 continues to move toward the valve seat 6, can bedetermined from conditions such as the maximum flow rate of the fluidpassing through the flow passage 5, the maximum value of the upstreampressure, and an output torque of the stepper motor 8. In other words,when the valve body 7 moves to the valve seat 6 side beyond the step-outboundary position, depending on an expansion condition of the shockabsorber 1, the resultant force of the upstream pressure and the fluidforce may overcome the torque of the stepper motor 8 such that step-outoccurs.

Hence, as shown in FIG. 3, using a step-out boundary position X, a zonebetween a seated position A and the step-out boundary position X is setas a step-out zone and a zone between the step-out boundary position Xand a maximum separation position B is set as a non-step-out zone. Thestep-out zone is a zone in which step-out may occur when the valve body7 is caused to move toward the valve seat 6 side by the stepper motor 8,as described above. The non-step-out zone, on the other hand, is a zonein which the torque of the stepper motor 8 is not overcome by theresultant force of the upstream pressure and the fluid force, andtherefore step-out does not occur even when the valve body 7 movestoward the valve seat 6 side.

In a case where the valve body 7 is positioned in the non-step-out zone,the stepper motor 8 does not step out even when the valve body 7approaches the valve seat 6. Indeed, when the valve body 7 is moved inthe separation direction from the valve seat 6, the resultant force ofthe upstream pressure and the fluid force acts in a direction forassisting separation of the valve body 7, and therefore the steppermotor 8 does not step out. Hence, when the valve body 7 is to be movedwithin the non-step-out zone, the stepper motor 8 should be energizedsuch that the valve body 7 moves by a desired movement distance. Morespecifically, the stepper motor 8 is driven by pulse signals transmittedat specific periods, and therefore, in the non-step-out zone, it issufficient to energize the stepper motor 8 by transmitting thereto aminimum number of pulse signals required to move the valve seat 7 by arequired distance, i.e. without taking step-out into consideration.

In a case where the valve seat 7 passes through the step-out zone to theseated position seated on the valve seat 6, on the other hand, thestepper motor 8 is energized to move the valve body 7 by a distance thatis at least twice the distance between the valve body 7 and the valveseat 6 while the valve seat 7 is in the step-out zone. Morespecifically, for example, when the valve body 7 is in the step-outzone, 48 pulse signals are required to move the valve body 7 by adistance for seating the valve body 7 on the valve seat 6 from aseparated position separated from the valve seat 6, and 100 pulsesignals can be generated per second, at least 96 pulse signals, i.e.twice the number of pulse signals required to move the valve body 7 bythe distance for seating the valve body 7 on the valve seat 6 from theseparated position separated from the valve seat 6, are applied to thestepper motor 8. An energization time corresponding to 96 pulse signalsis 0.96 seconds, and therefore the stepper motor 8 is energized for atleast 0.96 seconds.

Here, the shock absorber 1 expands and contracts repeatedly in responseto vibration input from a road surface while the saddle-ridden vehicletravels. As shown in FIG. 4, therefore, focusing on the vibration of theshock absorber 1 over a time t having an arbitrary length during travel,expansion operations and contraction operations are performed in equalnumbers. Meanwhile, the fluid flows through the flow passage 5 only whenthe shock absorber 1 performs the expansion operation.

Hence, when the valve body 7 is in the step-out zone in a situationwhere the valve body 7 has been driven from a condition in which theflow passage 5 is open such that the flow passage 5 is completelyblocked while travel is underway in the saddle-ridden vehicle and theshock absorber 1 is expanded due to vibration, the stepper motor 8 isenergized for a time required to move the valve body 7 twice thedistance needed to seat the valve body 7 on the valve seat 6. In thiscase, the contraction operation is underway in the shock absorber 1 forhalf the energization time, and therefore the fluid does not flowthrough the flow passage 5. Accordingly, the resultant force of theupstream pressure and the fluid force generated during fluid passagedoes not act on the valve body 7.

The stepper motor 8 is energized to move the valve body 7 by a distancethat is at least twice the distance from the separation position to theseated position seated on the valve seat 6. In other words, when thevalve body 7 is in the step-out zone and the valve body 7 is to bedriven to the seated position seated on the valve seat 6, theenergization time of the stepper motor 8 is set at no less than twicethe time required to move the valve body 7 by the distance from theseparated position to the seated position seated on the valve seat 6.

Hence, according to this invention, when the valve body 7 is in thestep-out zone, the energization time of the stepper motor 8 is set at noless than twice the time required to drive the valve body 7 by thedistance from the separated position to the seated position seated onthe valve seat 6. Further, since the fluid does not pass through theflow passage 5 for half the energization time, the valve body 7 can bedriven in a no-load condition, excluding a biasing force of the coilspring 19, during this time. As a result, the valve body 7 can be seatedreliably on the valve seat 6, thereby blocking the flow passage 5.

In other words, since the valve body 7 can be seated reliably on thevalve seat 6, step-out of the stepper motor 8 can be corrected. As aresult, step-out correction can be performed on the stepper motor 8 evenduring travel.

According to the shock absorber 1, therefore, the flow passage 5 can beblocked, enabling increases in the flow passage area adjustment width ofthe damping force adjustment mechanism V and the damping forceadjustment width. As a result, riding comfort on the vehicle can beimproved, and since step-out correction is performed even during travel,a desired damping force can be generated accurately.

Further, the torque required of the stepper motor 8 need only be largeenough to overcome the biasing force of the coil spring 19 so that thevalve body 7 can be pressed against the valve seat 6, and therefore alarge torque that can overcome the resultant force of the upstreampressure of the fluid passing through the flow passage 5 and the fluidforce is not required. Hence, the size of the stepper motor 8 does notneed to be increased even in a case where blockage of the flow passage 5is required. Moreover, since the size of the stepper motor 8 does nothave to be increased, the stepper motor 8 can be installed in thesaddle-ridden vehicle more easily, and a cost benefit is obtained.

Furthermore, when the valve body 7 is driven to separate from the valveseat 6 and when the valve body 7 is driven in the non-step-out zone, thestepper motor 8 need only be energized to move the valve seat 7 by anequal distance to the required movement distance of the valve seat 7,and therefore a damping force modification response is not impaired.

Further, in a case where the valve body 7 is caused to retreat from thevalve seat 6, the resultant force of the upstream pressure of the fluidpassing through the flow passage 5 and the fluid force acts in adirection for causing the valve body 7 to retreat from the valve seat 6not only when the shock absorber 1 is contracted such that the valveseat 7 is in a no-load condition but also when the shock absorber 1 isexpanded. Therefore, the stepper motor 8 does not step out while thevalve body 7 retreats. As a result, the valve body 7 can be positionedin a desired position reliably.

In the embodiment described above, a situation in which damping forceadjustment is performed continuously was described, but this inventionis not limited thereto, and damping force adjustment may be performed insteps. A case in which damping force adjustment is performed in stepswill now be described.

To adjust the damping force in steps, a valve body stop position must beset in advance within the non-step-out zone. The valve body stopposition is set in a plurality of positions depending on a number ofsteps by which damping force adjustment is to be modified. As shown inFIG. 5, for example, when the damping force is to be modified in threesteps, namely hard, medium, and soft, first, a condition in which thevalve body 7 is in the seated position A is set as a hard position. Thereason for this is that when the valve body 7 is in the seated positionA such that the flow passage 5 is blocked, maximum damping force isgenerated. Next, two valve body stop positions Y, Z at which a mediumdamping force and a soft damping force are respectively generated areset in the non-step-out zone. Hence, when the damping force is modifiedin three steps, the two valve body stop positions Y, Z in which thevalve body 7 stops are set in the non-step-out zone in addition to thecondition in which the valve body 7 is in the seated position A.

To ensure that the medium damping force is larger than the soft dampingforce, the medium valve body stop position Y of the valve body 7 isprovided further toward the valve seat 6 side than the soft valve bodystop position Z of the valve body 7. It should be noted that the softvalve body stop position Z does not have to be set in the maximumseparation position B.

When the valve body 7 is moved within the step-out zone in the seatingdirection toward the valve seat 6, the valve seat 7 is seated reliablyby energizing the stepper motor 8 in consideration of the possibility ofstep-out so that the valve body 7 is moved by a distance that is atleast twice the required movement distance. When the valve body 7 movestoward the valve seat 6 side in the step-out zone, however, the steppermotor 8 may or may not step out. Therefore, when a valve body stopposition is set in the step-out zone, the valve body 7 may not stop inthe set valve body stop position. Hence, the valve body stop positionsY, Z are provided in the non-step-out zone but not in the step-out zone.

When the valve body 7 is seated on the valve seat 6 from the mediumvalve body stop position Y, which is the closest position to thestep-out boundary position of the valve body stop positions Y, Z, thevalve body 7 is moved by at least twice the distance required to movethe valve seat 7 to the seated position A.

As regards movement of the valve body 7 in the separation direction fromthe seated position A, on the other hand, there is no danger of step-outoccurring during either movement of the valve body 7 through thestep-out zone or movement of the valve body 7 through the non-step-outzone, and therefore the stepper motor 8 is energized to move the valvebody 7 by the required movement distance.

When the damping force is modified from hard to medium, the steppermotor 8 does not step out, and therefore the stepper motor 8 isenergized to move the valve body 7 by a distance between the seatedposition A, which serves as the position of the valve body 7 when thedamping force is hard, and the medium valve body stop position Y.Further, when the damping force is modified from medium to soft or fromsoft to medium, the respective valve body stop positions Y, Z are set inthe non-step-out zone, and therefore there is no danger of step-out inthe stepper motor 8. Accordingly, the stepper motor 8 may be energizedto move the valve body 7 by a distance between the medium valve bodystop position Y and the soft valve body stop position Z.

When the damping force is modified from medium to hard, on the otherhand, the valve body 7 must be moved toward the valve seat 6 through thestep-out zone, in which the possibility of step-out occurring in thestepper motor 8 exists. Therefore, the stepper motor 8 is energized tomove the valve body 7 by twice the distance between the medium valvebody stop position Y and the seated position A serving as the positionof the valve body 7 when the damping force is hard. Further, when thedamping force is modified from soft to hard, the valve body 7 passesthrough the medium valve body stop position Y, and therefore thestepping motor 8 should be energized to move the valve body 7 by thedistance between the medium valve body stop position Y and the softvalve body stop position Z from the soft valve body stop position Z tothe medium valve body stop position Y, and the energized to move thevalve body 7 by at least twice the distance between the medium valvebody stop position Y and the seated position A in the zone extendingfrom the medium valve body stop position Y to the seated position Aserving as the position of the valve body 7 when the damping force ishard.

In a case where the medium valve body stop position Y is set in thenon-step-out zone rather than in the step-out boundary position Xserving as the boundary between the step-out zone and the non-step-outzone, and the valve body 7 is moved from the medium valve body stopposition Y to the seated position A, the valve body 7 moves to theseated position A by entering the step-out zone after passing throughthe non-step-out zone. In this case, the stepper motor 8 may beenergized to move the valve body 7 by the distance between the mediumvalve body stop position Y and the step-out boundary position X from themedium valve body stop position Y to the step-out boundary position X,and then energized to move the valve body 7 by m times (where m is anumber greater than 1) the distance between the step-out boundaryposition X and the seated position A after reaching the step-out zone.Further, the stepper motor 8 may be energized to move the valve body 7by m times the distance between the medium valve body stop position Yand the seated position A.

In both cases, the valve body 7 can be seated reliably on the valve seat6 even when the stepper motor 8 steps out midway. When the stepper motor8 is energized to move the valve body 7 by at least twice the distancebetween the medium valve body stop position Y and the seated position A,however, the energization time is longer, and therefore the valve body 7can be moved to the seated position more reliably, enabling animprovement in the reliability of step-out correction.

Furthermore, in the embodiment described above, damping force adjustmentis switched in three stages, but this invention is not limited thereto,and damping force adjustment may be switched in four or more stages.When a case in which the valve body 7 is in the seated position suchthat the flow passage 5 is closed is included in the number of stagesand the number of stages is set at N (where N is an integer of two ormore), N-1 valve body stop positions may be set in the non-step-outzone. When the valve body stop position closest to the step-out boundaryposition is set as a boundary stop position and the valve body 7 is tobe moved to the seated position, step-out correction can be performedreliably by energizing the stepper motor 8 to move the valve body 7 byat least twice the distance required to move the valve body 7 from theboundary stop position to the seated position.

In the embodiment described above, the damping force adjustmentmechanism V allows the fluid to pass through the flow passage 5 onlywhen the shock absorber 1 expands, and therefore functions as a dampingforce generation element that generates expansion side damping force inthe shock absorber 1. The damping force adjustment mechanism V istherefore capable of adjusting the expansion side damping force of theshock absorber 1. Alternatively, the damping force adjustment mechanismV may be set to allow the fluid to pass through the flow passage 5 onlywhen the shock absorber 1 contracts, thereby functioning as a dampingforce generation element that generates contraction side damping forcein the shock absorber 1 and adjusts the contraction side damping force.In other words, by configuring the connecting passage 4 d provided inthe piston coupling portion 4 c to connect the hollow portion 4 b to theexpansion side chamber R2 instead of the contraction side chamber R1,the damping force adjustment mechanism V can adjust the contraction sidedamping force. With this configuration, the flow passage 5 can be set toallow the fluid to pass only during the contraction operation of theshock absorber 1, and therefore the valve body 7 can be seated on thevalve seat 6 by energizing the stepper motor 8 to move the valve body 7by at least twice the distance required to seat the valve body 7 on thevalve seat 6, as described above. As a result, similar actions andeffects to those of the shock absorber 1 described above, in which theflow passage 5 is set to allow the fluid to pass only during expansion,can be obtained.

Further, the valve seat 6 is provided on the tip end of the piston rod4, and the valve housing 9 is provided to house the valve body 7. Theflow passage 5 penetrates the piston rod 4 and connects either thecontraction side chamber R1 or the expansion side chamber R2 in theshock absorber main body D to the reservoir R provided on the exteriorof the cylinder 2. The vehicle body side tube 10 is coupled to thevehicle body of the saddle-ridden vehicle, the axle side tube 11 iscoupled to the vehicle wheel of the saddle-ridden vehicle, the pistonrod 4 of the shock absorber main body D is coupled to the vehicle bodyside tube 10 via the valve housing 9, and the cylinder 2 is coupled tothe axle side tube 11. Furthermore, the stepper motor 8 is fixed to thevalve housing 9 and disposed to project from the vehicle body side tube10. As a result, the valve body 7 and the stepper motor 8 are disposedin close proximity, and therefore the valve body 7 can be driven withoutinterposing an elongated control rod or the like. Hence, the valve body7 can be driven to a desired position accurately, enabling animprovement in damping force controllability, and power feeding to thestepper motor 8 from the outside can be performed easily, leading toimprovements in convenience and versatility.

Moreover, respective structures of the valve body 7, the valve seat 6,and the flow passage 5 of the damping force adjustment mechanism V arenot limited to those described above, and may be subjected to designmodifications and alterations as long as the actions and effects of thisinvention are still obtained. For example, the valve body 7 is notlimited to a needle valve, and may be a poppet valve or the like.

Further, the shock absorber main body D may be configured either togenerate damping force only during expansion in a case where the dampingforce adjustment mechanism V generates damping force during expansion ofthe shock absorber 1, or to generate damping force only duringcontraction in a case where the damping force adjustment mechanism Vgenerates damping force during contraction of the shock absorber 1.

Although the invention has been described above with reference tocertain embodiments, the invention is not limited to the embodimentsdescribed above. Modifications and variations of the embodimentsdescribed above will occur to those skilled in the art, within the scopeof the claims.

The contents of Tokugan 2011-139045, with a filing date of Jun. 23, 2011in Japan, are hereby incorporated by reference.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A shock absorber comprising: a shock absorber main body having acylinder housing a fluid, a piston that is inserted into the cylinder tobe free to slide and divides an interior of the cylinder into acontraction side chamber and an expansion side chamber, and a piston rodinserted into the cylinder and coupled to the piston; and a dampingforce adjustment mechanism having a flow passage that allows the fluidfrom the cylinder to pass during only one of an expansion operation anda contraction operation of the shock absorber main body, a valve seatprovided midway in the flow passage, a valve body capable of advancingand retreating relative to the valve seat, and a stepper motor that isconfigured to adjust a flow passage area by driving the valve body toadvance and retreat relative to the valve seat, wherein a valve bodyposition in which step-out may occur in the stepper motor if the valvebody is moved further toward the valve seat therefrom is set as astep-out boundary position, and a zone between a seated position inwhich the valve body is seated on the valve seat and the step-outboundary position is set as a step-out zone, and when the valve body isto be moved to the seated position through the step-out zone, thestepper motor is energized to move the valve body by a distance that isat least twice a distance to the seated position.
 2. The shock absorberas defined in claim 1, wherein a zone between a maximum separationposition in which the valve body is maximally separated from the valveseat and the step-out boundary position is set as a non-step-out zone,and when the valve body is to be moved through the non-step-out zone,the stepper motor is energized to move the valve body by an equaldistance to a desired movement distance.
 3. The shock absorber asdefined in claim 1, wherein a plurality of valve body stop positions areset in the non-step-out zone and a valve body stop position closest tothe step-out boundary position, from among the plurality of valve bodystop positions, is set as a boundary stop position, and when the valvebody is to be moved to the seated position, the stepper motor isenergized to move the valve body by a distance that is at least twice adistance from the boundary stop position to the seated position.
 4. Theshock absorber as defined in claim 1, wherein the valve seat is providedon a tip end of the piston rod, and the flow passage penetrates thepiston rod and connects either the contraction side chamber or theexpansion side chamber in the shock absorber main body to a reservoirprovided on an exterior of the cylinder.
 5. The shock absorber asdefined in claim 4, further comprising: a vehicle body side tube coupledto a vehicle body of a saddle-ridden vehicle; an axle side tube coupledto a vehicle wheel of the saddle-ridden vehicle; and a valve housingthat houses the valve body, wherein the piston rod is coupled to thevehicle body side tube via the valve housing, the cylinder is coupled tothe axle side tube, and the stepper motor is fixed to the valve housingand disposed to project from an upper end opening portion of the vehiclebody side tube.